1. Field of the Invention
The present invention relates to the manufacture of fiberglass insulation materials, and more particularly to the preparation of phenolic binders for glass fibers.
2. Brief Description of the Prior Art
Aqueous dispersions of phenol-formaldehyde resole resins are frequently used in the manufacture of glass fiber insulation materials, such as insulative batts for walls, in roofs and ceilings, insulative coverings for pipes, and the like. Typically, after glass fiber has been formed, the still hot fiber is sprayed with aqueous binder dispersion in a forming chamber or hood, with the fibers being collected on a conveyer belt in the form of a wool-like mass associated with the binder. In some cases, a glass fiber web is sprayed with the aqueous dispersion. Urea-modified resole resins have been employed for this purpose, the urea contributing to the "punking" resistance of the binder (i.e., resistance to exothermic decomposition at elevated temperatures), and reducing volatiles liberated when the resin is cured at elevated temperature.
Frequently, in the manufacture of glass fiber insulation materials, the aqueous resole resin is prepared in advance of the preparation of the binder, or is supplied by a resin manufacturer, and stored until shortly before use. The resole is typically prepared by reaction of phenol and formaldehyde under basic conditions, the resulting reaction mixture being neutralized to a slightly basic pH by addition of a strong acid. Subsequently, the binder is prepared by adding to the resole resin urea, an acid catalyst for curing the resin and water to dilute the dispersion, and optionally other components, such as a silane glass-adhesion promoter and oil emulsion lubricant.
Preferably the binder is prepared by prereaction of the resole resin with urea at around ambient temperature to give a "premix" for the binder. Just before use, the binder is prepared by adding the remaining components.
The prereaction of the urea with the resole resin to form a premix presents logistical difficulties. In addition to storage facilities for the resole resin, urea and binder, additional facilities are needed for the premix. The timing of the preparation is also more complicated. In some cases, premix is preferably allowed to prereact for a minimum period after mixing and before the binder is prepared. Therefore, the demand for binder must be correctly anticipated to insure an adequate amount of premix is available, while avoiding a wasteful excess.
Ideally, all necessary urea would be added to the resole resin at the time of resin manufacture. This urea-modified resole resin would result in a simplified binder preparation without the logistical difficulties involved with premix preparation.
However, preparation of the urea-modified resole resin may result in downstream process difficulties, specifically the partial cure of the binder is manifested by reduction in the loft of the glass fiber mat just before the mat enters the curing oven and a tacky, over-dry feel to the mat. Further, the modification of the resole resin with the urea reduces the stability of the resin. There is a need for an improved process for preparing an urea-modified resole resin with greater stability, with significantly reduced precure of the resultant urea-modified resole resin-based binder, and enhanced shelf life.
The use of urea and ammonia as formaldehyde scavengers prior to neutralization of two-stage phenol-formaldehyde condensation resin is disclosed in U.S. Pat. No. 3,956,205. U.S. Pat. No. Re. 30,375 discloses the use of ammonia to raise the pH of a binder including a resole resin, urea and an acid catalyst for elevated temperature cure of the binder. U.S. Pat. No. 4,757,108 discloses a phenolic resole-urea composition made by reaction of urea with the free formaldehyde in the phenolic resole resin under acid conditions, the composition subsequently being made neutral or slightly basic by further addition of urea. U.S. Pat. No. 4,663,419 discloses phenol-formaldehyde-urea glass fiber sizing composition in which urea is added during cooling of the phenol-formaldehyde reaction mixture in order to reduce environmental pollution from free monomers.